Add missing include
Add ZeroCopyOutputStream and tidy up
Add write() to streambuf for protocol message
Split peer connect logic to another class (RIPD-711):
All of the logic for establishing an outbound peer connection including
the initial HTTP handshake exchange is moved into a separate class. This
allows PeerImp to have a strong invariant: All PeerImp objects that exist
represent active peer connections that have already gone through the
handshake process.
[FOLD] remove ConnectAttempt::write
[FOLD] more ConnectAttempt work